This invention relates generally to a method and structure for producing a Z-axis interconnection of printed wiring board elements and, more particularly, to a method and structure of providing a printed wiring board formed of a plurality of elements which are laminated together to form a printed wiring board having Z-axis interconnections.
Printed wiring boards are conventionally made up of a plurality of individual elements joined together to provide various levels of wiring on the surfaces of the elements and interconnections between the various wiring levels, such interconnection between the various levels often being referred to as Z-axis interconnections. In some conventional techniques for forming such interconnections in the Z-axis, a drilling operation is required after the various elements have been joined together. This requires precise alignment of all of the elements as well as precise drilling of the final structure which creates the possibility of misalignment at least requiring either rework of the board or at most scrapping of the board after it reaches this late assembly stage. Thus, it is desirable to provide elements for forming a printed wiring board and a technique for forming the elements in the printed wiring board which does not require drilling in the final stage but, rather, allows the individual elements to be formed with the components of the Z-axis connection which, when finally joined together, will provide the necessary connection between various layers of metal wiring.
According to the present invention, a method of forming a core member for a composite wiring board and a method of forming the composite wiring board, as well as the core member of the composite wiring board and the wiring board, are provided. The core member is formed by providing a dielectric substrate having opposite faces and forming an electrically conductive coating on at least one face thereof, preferably by laminating copper on the at least one face. At least one opening is formed through the substrate extending from one face to the other and through each conductive coating. An electrically conductive material is dispensed in each of the openings extending through the conducting coating. At least a portion of the surface of the conductive coating on at least one face is removed to allow a nub of the conductive material to extend above the substrate face and any remaining conductive material to thereby form a core that can be electrically joined face-to-face with a second core member or other circuitized structure. In one embodiment, a second core is then formed in a similar manner and the two cores joined face to face to provide a printed wiring board with electrical interconnections in the Z-axis, i.e. between the circuit traces on opposite faces of the circuit board so formed. In another embodiment, the core is used to join with at least one other circuitized member. The invention also contemplates a core member formed according to this invention and a printed wiring board formed using at least one core member.